Acid Sulphate Soil Interaction with Groundwater: A Remediation Case Study in East Trinity

Contaminated soil and groundwater resulting from pyrite oxidation occur in coastal areas throughout the world, but do not pose an issue unless allowed to oxidise as a result of drainage or excavation. The exposure and oxidisation of these soils increase the concentration of iron and aluminium ions and cause adverse impact on flora and fauna and also water quality. Depending on the climate conditions and scale of areas contaminated by acid sulphate soil (ASS), several remediation techniques (e.g. fixed-level weirs, two-way modified floodgates, permeable reactive barriers, etc.) can be employed to increase the pH near to neutral and prevent the oxidation of pyrite and production of extra acid.A case study of the East Trinity, the east of Cairns, Queensland, Australia is presented in this study. This region episodically discharges large amounts of acid resulting in periodic fish kills. To remediate the ASS issue, a lime-assisted tidal exchange strategy had been undertaken by the local government. As a result, the quality of water improved and the pH increased from 3.5 to 6-8 and also the rate of aluminium and iron reduced to neutral values.